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Doctoral thesis2021Open access

Diversity and functional potential of fungal communities in Arctic and boreal freshwaters

Kluge, Mariana


Fungi are important decomposers of the organic matter (OM) in terrestrial environments, but there is limited knowledge about their ecological roles in aquatic ecosystems. This thesis applies a variety of molecular techniques (e.g. metabarcoding, sequencing of genomes and metagenomics) to explore the diversity of freshwater fungi and their role in the recycling of organic matter. The aquatic fungal diversity was first assessed in boreal lakes in Scandinavia. The composition of the communities varied significantly across lakes, and was associated with organic carbon availability. Furthermore, the relationship between fungal diversity and OM was extensively explored in permafrost ecosystems. Climate change is causing the thawing and collapse of permafrost peatlands, creating water bodies named thermokarst ponds. These ponds receive a significant amount of carbon previously stored in the permafrost, and are considered hotspots for carbon cycling. To investigate the ecology of the fungi in these ponds, five regions across the Arctic were sampled, comprising a gradient of permafrost integrity: from sites not affected by thawing to degraded sites with thermokarst ponds. The quality of the dissolved organic matter (DOM) was strongly linked with the fungal community composition, and associated with a significant decline in beta-diversity towards the degraded sites. Also, the genetic functional potential of the fungal communities in the pond water and sediment was explored at one of the degraded sites. The results showed the highest potential for breaking down the OM in the sediment, associated with higher relative abundances of fungal isolates with greater potential for degradation of plant litter. On the contrary, in the water, the fungi had a high potential for growth. Correlations between genes and proxies for the water DOM quality were found, suggesting that the aquatic fungi are able to benefit from the freshly produced OM of microbial sources and old OM from terrestrial sources. These findings shed light onto the ecological roles of aquatic fungal communities in the carbon cycle of ecosystems affected by a warming climate.


aquatic fungi; Arctic ponds; boreal lakes; thawing permafrost; carbon cycling; fungal diversity; functional potential; climate change

Published in

Acta Universitatis Agriculturae Sueciae
2021, number: 2021:71
ISBN: 978-91-7760-819-6, eISBN: 978-91-7760-820-2
Publisher: Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences